I have an 07 lbz and about 2 months ago is when I noticed this problem. I started my truck and it flashed low coolant level. Went and checked my tank, added some, and was fine. Bout 3 weeks ago same problem happened. Went and looked and my cap was all clogged with black stuff. I'm guessing soot. So I went and bought a new cap. Last night same problem. Time to get this fixed. I ran truck for about 3 hours and let it sit overnight. Went and felt the upper hose and I could squeez it almost together. Went and unscrewed cap and released pressure and the hose was super super easy to squeeze. I have an egt blocker plate on my truck. Efi live, intake and exhaust. My truck leaks nothing.

I sorry you're having issues with your coolant levels. I would like to do research on your concern and offer my assistance. Could you please private message me your name, address, vehicle identification number, and current mileage?

I sorry you're having issues with your coolant levels. I would like to do research on your concern and offer my assistance. Could you please private message me your name, address, vehicle identification number, and current mileage?

Thank you,

Jessica L.
GM Customer Care

LOL

I always find this type of post funny. These trucks there out of warranty from mileage and years. Hell I work for Gm had a driver side seat about made me crash the truck from the frame breaking dealer gave two shits about the safety issue there. Needs a set of injectors I think we can put that under the emissions warranty in good faith

Pressure test and take a look. There are several places up top that can leak while driving and never leave a puddle while parked. Very likely source is the plastic quick-connects used on the heater hoses at the firewall.

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